Method for forming vertical spacers for spacer-defined patterning

ABSTRACT

A method of forming vertical spacers for spacer-defined multiple patterning, includes: depositing a first conformal pattern-transfer film having a first film stress, and continuously depositing a second conformal pattern-transfer film having a second film stress on a template; dry-etching the template except for a core material and a vertical portion of the first and second pattern-transfer films to form vertical spacers; and dry-etching the core material, forming a vacant space between the vertical spacers, wherein by adjusting the difference in film stress between the first and second pattern-transfer films, the leaning angle of the spacers is adjusted.

BACKGROUND Field of the Invention

The present invention relates generally to a method for forming verticalspacers for spacer-defined patterning in semiconductor fabricationprocesses.

Related Art

Patterning processes using lithography technology are essential tosemiconductor fabrication processes. However, lithography technologyfaces difficulties in pattern miniaturization due to the limitedwavelength of a laser light used in lithography. One approach to realizepattern miniaturization using known patterning technology is SADP (SelfAligned Double Pattering) or SDDP (Spacer-Defined Double Patterning).FIG. 4 is a schematic representation of double patterning (steps (a) to(c)) according to a comparative example. In step (a), mandrels(photoresist) 101 are patterned as a core material on an underlyinglayer 102. In step (b), a film 103 is deposited to cover the exposedsurfaces of the mandrels 101 and the exposed surface of the underlyingsurface 102 in their entirety. In step (c), by dry etching, thehorizontal portions of the film 103 and the mandrels 101 are etched soas to form spacers 104. By using the above process, a patternconstituted by the spacers 104 in step (c) can have a pitch which is ahalf of that of the pattern of the photoresist 101 in step (a), i.e.,double-dense pitched patterning can be accomplished. However, in theprocess, the spacers 104 (formed from the sidewall portions of the film103) lean toward a vacant space 110 during and after the core-strippingstep (c) as shown in FIG. 4. This leaning phenomenon makes it difficultfor semiconductor manufacturers to continuously conduct subsequentintegration processes precisely. It is expected that the above leaningproblem will become more serious as technology advances andminiaturization progresses.

There is another problem in the above conventional patterningillustrated in FIG. 4. That is, since the spacers 104 are formed fromthe film 103 deposited on the mandrels 101, and the film 103 depositedat the top corners of each mandrel 101 is necessarily curved as shown instep (b), a top portion 111 of the spacer 104 formed from the top cornerportion of the film 103 becomes naturally rounded while being subjectedto etching in step (c). Further, in the etch-back process of step (c),the rounded profile of the spacer 104 becomes more manifest andsignificant because the top portion of the spacer is attacked by ionbombardment from a plasma (wherein an outer part of the spacer is morevulnerable to ion bombardment than an inner part of the spacer), causing“shoulder loss”. If the shoulder loss is significant, the top portion ofthe spacer needs to be trimmed, thereby decreasing the height of thespacer. This shoulder loss phenomenon makes it difficult forsemiconductor manufacturers to continuously conduct subsequentintegration processes precisely. It is expected that the above shoulderloss problem will become more serious as technology advances andminiaturization progresses.

Any discussion of problems and solutions in relation to the related arthas been included in this disclosure solely for the purposes ofproviding a context for the present invention, and should not be takenas an admission that any or all of the discussion was known at the timethe invention was made.

SUMMARY

In order to solve at least one of the problems in the conventionalpatterning, in some embodiments of the present invention, the spacersare formed by using a two-layer film, thereby controlling the leaningangle of the etched spacers, particularly inhibiting or suppressing thespacers from inwardly leaning, which angle is defined as an angle of aninner face of each sidewall portion as measured with reference to a linevertical to a bottom of a vacant space which is formed by removing acore material between the spacers, wherein a leaning angle of zerorepresents completely vertical and a leaning angle of a positive valuerepresents leaning inward. The two-layer film satisfies the conditionsthat the two layers have different film stresses and both are highlyconformal (preferably formed by atomic layer deposition, ALD). Bychanging the difference in film stress between the two layers, theleaning angle of the spacer can be controlled to a desired degree and ina desired direction (inward or outward). That is, by adjusting the outerlayer to have more compressive stress than the inner layer (i.e., theouter layer has a greater value of stress in the negative direction thandoes the inner layer), the leaning angle of the spacer becomes greaterin the positive direction, i.e., leaning inward. On the other hand, byadjusting the inner layer to have more compressive stress than does theouter layer (i.e., the inner layer has a greater value of stress in thenegative direction than does the outer layer), the leaning angle of thespacer becomes greater in the negative direction, i.e., leaning outward.As such, by properly adjusting the difference in film stress between theinner and outer layers constituting the spacer, the leaning angle of thespacer can be adjusted to a target value.

Further, in some embodiments, the two-layer film satisfies theconditions that the two layers have different degrees of resistance todry etching. By changing the difference in dry etch rate between the twolayers, the top profile of the spacer can be manipulated. Particularly,by adjusting the inner layer to have less resistance to dry etching (ahigher dry etch rate) than does the outer layer, shoulder loss caneffectively be prevented, and the top of the spacer can becomesubstantially flat when the spacer is formed. Thus, further etching tomake the top of the spacer flat can be omitted, i.e., the effectiveheight of the spacer can be maintained which height may vary dependingon the target structure, the patterning method, etc. Accordingly, whenthe spacer is used as mask, a thick underlying layer can be processed.Further, by depositing another a pattern-transfer film on the spacers,followed by anisotropic etching, self-aligned quadruple patterning(SAQP) or spacer-defined quadruple patterning (SDQP) (spacer on spacer)can effectively be performed. By this, applications of the spacers canbe broadened. In SAQP or SDQP, dividing the pitch of the spacers isperformed twice, thereby increasing resolution to 11 nm HP (half pitch).

For purposes of summarizing aspects of the invention and the advantagesachieved over the related art, certain objects and advantages of theinvention are described in this disclosure. Of course, it is to beunderstood that not necessarily all such objects or advantages may beachieved in accordance with any particular embodiment of the invention.Thus, for example, those skilled in the art will recognize that theinvention may be embodied or carried out in a manner that achieves oroptimizes one advantage or group of advantages as taught herein withoutnecessarily achieving other objects or advantages as may be taught orsuggested herein.

Further aspects, features and advantages of this invention will becomeapparent from the detailed description which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of this invention will now be described withreference to the drawings of preferred embodiments which are intended toillustrate and not to limit the invention. The drawings are greatlysimplified for illustrative purposes and are not necessarily to scale.

FIG. 1 is a schematic representation of a PEALD (plasma-enhanced atomiclayer deposition) apparatus for depositing a protective film usable inan embodiment of the present invention.

FIG. 2 is a flowchart illustrating steps of fabricating a verticalspacer structure according to an embodiment of the present invention.

FIG. 3 is a flowchart illustrating steps of adjusting the shape of avertical spacer structure according to another embodiment of the presentinvention.

FIG. 4 is a schematic representation of double patterning (steps (a) to(c)) according to a comparative example.

FIG. 5 is a schematic representation of double patterning (steps (a) to(c)) according to an embodiment of the present invention.

FIG. 6 is a schematic representation of double patterning (steps (a) to(c)) according to another embodiment of the present invention.

FIG. 7 is a STEM (Scanning Transmission Electron Microscope) photographof a cross sectional view of spacers fabricated on a substrate accordingto an embodiment of the present invention, which photograph is annotatedto show a leaning angle.

FIG. 8 shows STEM photographs of cross-sectional views wherein (a) and(b) show silicon oxide films having different film stress deposited onresist patterns, and (c) and (d) show spacers formed from the filmsshown in (a) and (b), respectively.

FIG. 9 shows STEM photographs of cross-sectional views wherein (a) and(b) show the spacers shown in (c) and (d) of FIG. 8, respectively, and(c) shows a deposited silicon oxide film consisting of an inner siliconoxide layer used for the spacers shown in (a) and an outer silicon oxidelayer used for the spacers shown in (b), (d) shows spacers formed fromthe film shown in (c), (e) shows a deposited silicon oxide filmconsisting of an inner silicon oxide layer used for the spacers shown in(b) and an outer silicon oxide layer used for the spacers shown in (b),and (f) shows spacers formed from the film shown in (e), according toembodiments of the present invention.

FIG. 10 is a graph showing the relationship between the leaning angleand difference in film stress between the outer layer and inner layer ofa two-layer pattern-transfer film according to embodiments of thepresent invention.

FIG. 11 shows STEM photographs of cross-sectional views annotated toshow “shoulder loss”, wherein (a) shows spacers formed from a one-layerfilm according to a comparative example, and (b) shows spacers formedfrom a two-layer film according to an embodiment of the presentinvention.

FIG. 12 illustrates a mechanism of forming a spacer having a flat topwherein (a) schematically illustrates a two-layer film used for formingthe spacer, and (b) to (f) are enlarged schematic partial views showingsteps according to an embodiment of the present invention.

FIG. 13 shows STEM photographs of cross-sectional views showing steps offorming spacers having a flat top from a two-layer film in steps (a) to(f) according to an embodiment of the present invention.

FIG. 14 is a schematic representation of pattern transfer and targetetching (steps (a) to (j)) using spacer-defined double patterning (SDDP)according to an embodiment of the present invention.

FIG. 15 is a flowchart illustrating steps of adjusting the top profileof a vertical spacer structure according to another embodiment of thepresent invention.

FIG. 16 illustrates a process sequence in one cycle of deposition of asilicon oxide film having a different film stress according to anembodiment of the present invention.

FIG. 17 illustrates a process sequence in one cycle of deposition of asilicon nitride film having a different film stress according to anembodiment of the present invention.

FIG. 18 is a schematic representation of vertical spacers for explainingmechanics of vertical spacers when the spacer is constituted by multiplelayers (the number of layers is n).

FIG. 19 is a schematic representation of vertical spacers for explainingmechanics of vertical spacers when the spacer is constituted by twolayers.

DETAILED DESCRIPTION OF EMBODIMENTS

In this disclosure, “gas” may include vaporized solid and/or liquid andmay be constituted by a single gas or a mixture of gases. In thisdisclosure, a process gas introduced to a reaction chamber through ashowerhead may be comprised of, consist essentially of, or consist of aprecursor gas and an additive gas. The precursor gas and the additivegas are typically introduced as a mixed gas or separately to a reactionspace. The precursor gas can be introduced with a carrier gas such as anoble gas. The additive gas may be comprised of, consist essentially of,or consist of a reactant gas and a dilution gas such as a noble gas. Thereactant gas and the dilution gas may be introduced as a mixed gas orseparately to the reaction space. A precursor may be comprised of two ormore precursors, and a reactant gas may be comprised of two or morereactant gases. The precursor is a gas chemisorbed on a substrate andtypically containing a metalloid or metal element which constitutes amain structure of a matrix of a dielectric film, and the reactant gasfor deposition is a gas reacting with the precursor chemisorbed on asubstrate when the gas is excited to fix an atomic layer or monolayer onthe substrate. “Chemisorption” refers to chemical saturation adsorption.A gas other than the process gas, i.e., a gas introduced without passingthrough the showerhead, may be used for, e.g., sealing the reactionspace, which includes a seal gas such as a noble gas. In someembodiments, “film” refers to a layer continuously extending in adirection perpendicular to a thickness direction substantially withoutpinholes to cover an entire target or concerned surface, or simply alayer covering a target or concerned surface. In some embodiments,“layer” refers to a structure having a certain thickness formed on asurface or a synonym of film or a non-film structure. A film or layermay be constituted by a discrete single film or layer having certaincharacteristics or multiple films or layers, and a boundary betweenadjacent films or layers may or may not be clear and may be establishedbased on physical, chemical, and/or any other characteristics, formationprocesses or sequence, and/or functions or purposes of the adjacentfilms or layers.

Further, in this disclosure, the article “a” or “an” refers to a speciesor a genus including multiple species unless specified otherwise. Theterms “constituted by” and “having” refer independently to “typically orbroadly comprising”, “comprising”, “consisting essentially of”, or“consisting of” in some embodiments. Also, in this disclosure, anydefined meanings do not necessarily exclude ordinary and customarymeanings in some embodiments.

Additionally, in this disclosure, any two numbers of a variable canconstitute a workable range of the variable as the workable range can bedetermined based on routine work, and any ranges indicated may includeor exclude the endpoints. Additionally, any values of variablesindicated (regardless of whether they are indicated with “about” or not)may refer to precise values or approximate values and includeequivalents, and may refer to average, median, representative, majority,etc. in some embodiments.

In the present disclosure where conditions and/or structures are notspecified, the skilled artisan in the art can readily provide suchconditions and/or structures, in view of the present disclosure, as amatter of routine experimentation. In all of the disclosed embodiments,any element used in an embodiment can be replaced with any elementsequivalent thereto, including those explicitly, necessarily, orinherently disclosed herein, for the intended purposes. Further, thepresent invention can equally be applied to apparatuses and methods.

The embodiments will be explained with respect to preferred embodimentsin various aspects. However, the present invention is not limited to thepreferred embodiments.

Some embodiments are directed to a method of forming spacers forspacer-defined patterning in steps comprising (i) depositing apattern-transfer film on a template having a surface patterned by amandrel formed on an underlying layer, (ii) dry-etching the templatewhose entire upper surface is covered with the pattern-transfer film,and thereby selectively removing a top portion of the pattern-transferfilm formed on a top of the mandrel and a horizontal portion of thepattern-transfer film formed on the underlying layer while leaving themandrel as a core material and sidewall portions of the pattern-transferfilm formed on sidewalls of the mandrel as spacers, and (iii)dry-etching the core material, forming a vacant space, whereby thetemplate has a surface patterned by the spacers on the underlying layer,which spacers lean inwardly toward the vacant space at a first leaningangle which is defined as an angle of an inner face of each sidewallportion as measured with reference to a line vertical to a bottom of thevacant space wherein a leaning angle of zero represents completelyvertical and a leaning angle of a positive value represents leaninginward.

In the above, the improvement comprises: in step (i), depositing, as thepattern-transfer film, a conformal pattern-transfer film havingdifferent film stresses in a depth direction wherein a lower half of theconformal pattern-transfer film has a first film stress and an upperhalf of the conformal pattern-transfer film has a second film stress,wherein the first film stress is more compressive than the second filmstress, whereby in step (iii), the spacers lean less inwardly toward thevacant space at a second leaning angle which is less than the firstleaning angle. The lower half and the upper half of the pattern-transferfilm constitute a two-layer film.

In this disclosure, a “two-layer” film or spacer may refer to a film orspacer having a two-layer structure wherein when mathematically,geographically, or virtually dividing the structure into a lower halfand an upper half in a thickness (or depth) direction, the lower andupper halves, each as a whole, have differences in physical, chemical,and/or any other characteristics or properties, compositions ormaterials, and/or formation processes, wherein (a) the differences aremanifested in the thickness direction discontinuously at a discrete (ordetectable) boundary (or interface) formed between two adjacent discretelayers included in the lower and upper halves wherein the discreteboundary exists in the lower half or the upper half or at a virtualboundary between the lower and upper halves; (b) the differences aremanifested in the thickness direction continuously without a discrete(or detectable) boundary (or interface) wherein the physical, chemical,and/or any other characteristics or properties, compositions ormaterials, and/or formation processes are gradually (substantiallywithout discontinuity points) changed in the thickness direction; or (c)the differences are manifested in the thickness direction in a mannerdescribed in (a) and (b) in any combination. In some embodiments, thetwo-layer structure is constituted by two discrete layers satisfying (a)wherein the discrete boundary exists in the lower half or the upper halfor at the virtual boundary between the lower and upper halves, whereineach layer may be constituted by a single layer or multiple layerssatisfying (a), (b), or (c) above. In some embodiments, the two-layerfilm may consist of two single films. The phrase “consisting of”signifies exclusion of unrecited components. However, “consisting of”does not exclude additional components that are unrelated to theinvention such as natural oxidation film ordinarily associatedtherewith. The two-layer film may be in contact with other film.However, the other film does not constitute a part of the two-layer filmsince the other film does not constitute a part of the vertical spacer.

In this disclosure, the term “conformal” may generally refer topreserving the correct angles between directions within small areas,e.g., maintaining the angle at a corner of a mandrel (core material)when depositing a pattern-transfer film on the mandrel so as to form afilm along the sidewall of the mandrel, which film has a substantiallyuniform thickness along the sidewall, regardless of the thickness offilm deposited on the top of the mandrel. In some embodiments,“conformal” refers to a ratio of thickness of film at a center depositedon the sidewall to thickness of film at a center deposited on the topbeing close to one (e.g., 1±0.2 or less), which is indicative of forminga film along the sidewall of the mandrel, which film has a substantiallyuniform thickness along the sidewall (“substantially uniform” refers toa maximum difference being less than 20% or less or 10% or less).

In some embodiments, the conformal pattern-transfer film is constitutedby multiple layers (e.g., 2 to 6 discrete layers).

In some embodiments, the multiple layers are constituted by a firstlayer and a second layer deposited on the first layer, wherein the firstlayer has a film stress which is more compressive than a film stress ofthe second layer, and the first layer has a thickness which is 25% to75% (e.g., 40% to 65%) of a total thickness of the first and secondlayers. The thickness of the first and second layers may be set in orderto adjust the eventual leaning angle of the layers. That is, the greaterthe thickness of the layer, the higher the deformation force of thelayer becomes, because the thicker layer is not easily bent and also canexert more deformation force on the other layer. For example, a changeof the leaning angle can be manipulated by changing S₁, T₁, S₂, and T₂(wherein S₁ and T₁ are film stress and thickness of the first layer,respectively, whereas S₂ and T₂ are film stress and thickness of thesecond layer, respectively) using the following factor:

F=(S ₁ −S ₂)×(T ₁ ×T ₂)/(T ₁ +T ₂)³  (1)

For example, when T₁/T₂=4/6, the leaning angle can be estimated to bedecreased by 4% as compared with that when T₁/T₂=5/5 (i.e.,[(5×5)/(5+5)³−(4×6)/(4+6)³]/[(5×5)/(5+5)³]=0.04). Similarly, whenT₁/T₂=3/7, 2/8, and 1/9, the leaning angle can be estimated to bedecreased by 16%, 36%, and 64%, respectively, as compared with that whenT₁/T₂=5/5. Thus, when T₁/T₂ is approximately 4/6 or greater but lessthan 5/5, the leaning angle is expected to be substantially the same asthat when T₁/T₂=5/5. On the other hand, when T₁/T₂ is approximately 2/8or smaller, the leaning angle is expected to be significantly smallerthan that when T₁/T₂=5/5. Accordingly, the eventual leaning angle can beadjusted by changing the thickness of each layer when using multiplelayers having different film stress values.

Equation (1) above can be derived as follows. FIG. 18 is a schematicrepresentation of vertical spacers for explaining mechanics of verticalspacers when the spacer is constituted by multiple layers (the number oflayers is n). FIG. 19 is a schematic representation of vertical spacersfor explaining mechanics of vertical spacers when the spacer isconstituted by two layers. As illustrated in FIG. 18, it is assumed thata spacer 111 formed on a substrate 110 is constituted by n layers (n isan integer) wherein the X-axis is set in a thickness direction of thelayers. When the spacer 111 is tilted inward, stress σ_(L) imparted bytilting to the spacer at thickness x (an inner layer is compressedwhereas an outer layer is stretched with reference to a boundary set atthickness x) can be expressed as σ_(L)=ax+b (a, b are constants;particularly, a is proportional to an leaning angle). Stress σ_(C)generated by the material of the spacer can be expressed as σ_(C)=σ₁(0<x<t₁), σ₂ (t₁<x<t₂), σ_(n) (t_(n-1)<x<t). Stress σ(x) at thickness xis a sum of the above two components (i.e., σ_(L)(x) and σ_(C)(x)).Thus, potential energy W(x) at thickness x can be expressed asW(x)∝{σ_(L)(x)+σ_(C)(x)}². For the entire spacer, potential energyW_(total) can be obtained by integrating the above with respect to x asW_(total)=∫₀ ^(t)W(x)dx∝∫₀ ^(t){σ_(L)(x)+σ_(C)(x)}²dx. The potentialenergy has a minimum value, i.e., W_(total)(a, b)=minimum. Accordingly,the following simultaneous equations can be obtained, and by solving theequations, values of a, b, and leaning angle can be estimated:

∂W _(total)(a,b)/∂a=0,∂W _(total)(a,b)/∂b=0  (2)

In the above, when the spacer is constituted by two layers asillustrated in FIG. 19, a solution of simultaneous equations (2) isderived as follows:

a=6(σ₁−σ₂)(t−t ₁)(t ₁ /t ³)  (3)

Equation (1) is the same as equation (3) where T₁=t₁, (T₁+T₂)=t, S₁=σ₁,S₂=σ₂, and F=a/6. According to equation (1) or (3), in a configurationwhere the spacer is constituted by two layers having different stressvalues, and the total thickness is constant, when a ratio of thicknessof layer A to thickness of layer B is 1/1, the difference in leaningangle with reference to the leaning angle of a spacer constituted by asingle layer becomes maximum, and when the ratio is other than 1/1, theleaning angle of the spacer constituted by two layers becomes closer tothat of the spacer constituted by a single layer, wherein the eventualleaning angle of the spacer can be estimated based on “F” of equation(1) as discussed above.

In some embodiments, the thickness of the first layer is equal to orgreater than the thickness of the second layer. The total thickness ofthe pattern-transfer film may widely vary depending on the resolution oflithography, the intended application of the spacer, etc., and maytypically be in a range of approximately 3 nm to approximately 40 nm(more typically approximately 10 nm to approximately 40 nm). Accordingto a non-limiting theory, by setting the thickness of the first layerwhich is equal to or greater than the thickness of the second layer,while the top of the inner layer (the inner layer) of the spacer is moreeasily etched by ion bombardment from a plasma than the outer layer (thesecond layer) of the spacer, the top of the outer layer is alsoirradiated with reflected ion irradiation by the etched surface of theinner layer, promoting the etching of the top of the outer layer andadvancing flattening the top of the spacer.

In some embodiments, the conformal pattern-transfer film has film stressvarying in the depth direction, wherein the film stress gradually orcontinuously increases in an outward direction. The gradual orcontinuous increase of film stress can be determined using anapproximation straight or curved line drawn in a cross sectional view ofthe pattern-transfer film (localized discontinuous points can exist). Insome embodiments, the gradual or continuous increase of film stress canbe observed in the entire thickness of the pattern-transfer film. Insome embodiments, the gradual increase of film stress is an increase insteps (intermittent increase in the thickness direction). In the above,the pattern-transfer film may be constituted by a single discrete filmhaving a same composition or multiple different discrete films havingdifferent compositions.

In some embodiments, a difference between the film stress of the firstlayer and the film stress of the second layer is between approximately150 MPa and approximately 800 MPa (e.g., approximately 200 MPa toapproximately 600 MPa).

In some embodiments, the first and second layers are independentlyconstituted by any suitable material such as silicon oxide, siliconnitride, silicon carbide, titanium oxide, and titanium nitride, etc.Silicon oxide is characterized primarily by Si—O bonds but can alsocontain carbon atoms, hydrogen atoms, and other insubstantial componentssuch as unavoidable impurities associated with the deposition process,and silicon nitride is characterized primarily by Si—N bonds but canalso contain carbon atoms, hydrogen atoms, and other insubstantialcomponents such as unavoidable impurities associated with the depositionprocess. In some embodiments, the first and second layer are constitutedby different compositions; for example, the first layer is constitutedby silicon nitride and the second layer is silicon oxide. In someembodiments, the first and second layers are constituted by a samecompositions such as silicon oxide.

Film stress of each pattern-transfer film can be adjusted bymanipulating the deposition conditions. For example, as for a siliconoxide film, by inserting n times (n is an integer) a sub-cycle whereinthe template is exposed to an argon plasma without oxygen, in one cycleof PEALD wherein the template is exposed to an oxygen-argon plasmatypically once, the film stress can be adjusted. For example, as for asilicon nitride film, by changing the duration of an RF power pulseand/or the applied RF power in one cycle of PEALD, the film stress canbe adjusted. By manipulating the above parameters, the film stress canbe adjusted to be constant or changed in steps or continuously in thethickness direction.

In some embodiments, the second leaning angle is in a range ofapproximately −1 degree to approximately 1 degree (in other embodiments,in a range of approximately −1 degree to approximately 2 degrees). Theleaning angle is defined as an angle formed at an intersecting pointbetween a line representing the inner face of the sidewall portion ofthe spacer on in a cross sectional view and a line vertical to a linerepresenting the bottom face of the vacant space in the cross sectionalview. The line representing the inner face is an approximation straightline representing the inner face passing through the intersecting pointin the cross sectional view. The line representing the bottom face is anapproximation straight line representing the bottom face passing throughthe intersecting point in the cross sectional view. When the leaningangle is zero, the inner face of the spacer is completely vertical tothe bottom face, when the leaning angle is a positive value, the innerface of the spacer leans inward, and when the leaning angle is anegative value, the inner face of the spacer leans outward.

In some embodiments, the multiple layers are deposited byplasma-enhanced atomic layer deposition (PEALD) which is capable ofdepositing a highly conformal film (e.g., a conformality of 80% orhigher or 90% or higher).

In some embodiments, the first layer has less resistance to dry etchingthan does the second layer. By manipulating resistance to dry etching ofthe first and second layers, the top profile of the vertical spacer canbe adjusted. In some embodiments, a difference in resistance to dryetching between the first layer and the second layer is such that instep (ii) (of dry-etching the template) which is an etchback process, atop of each spacer becomes substantially flat by inhibiting shoulderloss of the spacer by dry etching. The resistance to dry etchingindicates how fast or slow the spacer material is etched (i.e., dry etchrate) during an etchback process using a plasma. In some embodiments,the difference in dry etch rate between the first and second layers isin a range of approximately 0.05 nm/sec. to approximately 0.5 nm/sec.,typically approximately 0.1 nm/sec. to 0.3 nm/sec., so as to effectivelyflatten the top of the vertical spacer. In some embodiments, for theetchback process by a plasma (step (ii)), a fluorine-containing etchantsuch as CF₄, CHF₃, or C₄F₈ is used in combination with argon (foretching silicon nitride, additionally oxygen), whereas for a strippingprocess (ashing process) by a plasma (step (iii)), oxygen or argon gasis used as an etchant. For etching a pattern-transfer film constitutedby a silicon oxide outer layer and a silicon nitride inner layer, first,the silicon oxide outer layer is etched under conditions set for etchingsilicon oxide, and then after a time period set for removing the siliconoxide outer layer from the top of the mandrel, the silicon nitride innerlayer is etched under conditions set for etching silicon nitride. Insome embodiments, during the stripping process, the flattening of thetop of the vertical spacer progresses continuously.

In another aspect, some embodiments are directed to a method of formingspacers for spacer-defined patterning in steps comprising (i) depositinga pattern-transfer film on a template having a surface patterned by amandrel formed on an underlying layer, (ii) dry-etching the templatewhose entire upper surface is covered with the pattern-transfer film,and thereby selectively removing a top portion of the pattern-transferfilm formed on a top of the mandrel and a horizontal portion of thepattern-transfer film formed on the underlying layer while leaving themandrel as a core material and sidewall portions of the pattern-transferfilm formed on sidewalls of the mandrel as spacers, and (iii)dry-etching the core material, forming a vacant space, whereby thetemplate has a surface patterned by the spacers on the underlying layer,which spacers lean outwardly away from each other at a first leaningangle which is defined as an angle of an inner face of each sidewallportion as measured with reference to a line vertical to a bottom of thevacant space wherein a leaning angle of zero represents completelyvertical and a leaning angle of a negative value represents leaningoutward.

In the above, the improvement comprises: in step (i), depositing, as thepattern-transfer film, a conformal pattern-transfer film havingdifferent film stresses in a depth direction wherein a lower half of theconformal pattern-transfer film has a first film stress and an upperhalf of the conformal pattern-transfer film has a second film stress,wherein the first film stress is more tensile than the second filmstress, whereby in step (iii), the spacers lean less outwardly away fromeach other at a leaning angle which is greater than the first leaningangle. When the vertical spacer tends to lean outward in a directiondecreasing the leaning angle, the embodiments disclosed herein also canapply, thereby forming the vertical spacer having a leaning angle ofsubstantially zero (e.g., ±1 degree).

In still another aspect, some embodiments are directed to a method offorming vertical spacers for spacer-defined multiple patterning,comprising: (i) providing a template having a surface patterned by amandrel formed on an underlying layer in a reaction space; (ii)depositing a first conformal pattern-transfer film having a first filmstress, and continuously depositing a second conformal pattern-transferfilm having a second film stress on the entire patterned surface of thetemplate, wherein the first and second film stresses are different;(iii) dry-etching the template whose entire upper surface is coveredwith the first and second pattern-transfer films, and therebyselectively removing a portion of the first and second pattern-transferfilms formed on a top of the mandrel and a horizontal portion of thefirst and second pattern-transfer films while leaving the mandrel as acore material and a vertical portion of the first and secondpattern-transfer films as vertical spacers; and (iv) dry-etching thecore material, forming a vacant space between the vertical spacers,whereby the template has a surface patterned by the vertical spacers onthe underlying layer.

In some embodiments, the above method further comprises: (v) measuring aleaning angle of the vertical spacer, which is defined as an angle of aninner face of the vertical spacer facing the vacant space as measuredwith reference to a line vertical to a bottom of the vacant spacewherein a leaning angle of zero represents completely vertical and aleaning angle of a positive value represents leaning inward, followed byjudging whether the leaning angle is within a target range; (vi)conducting again steps (i) to (iv): (a) without changes to form finalvertical spacers if the leaning angle is within the target range; (b)with changes wherein, as the first conformal pattern-transfer film instep (ii), a conformal pattern-transfer film having higher compressivestress than the first film stress by a measurable degree is deposited,and/or, as the second conformal pattern-transfer film in step (ii), aconformal pattern-transfer film having higher tensile stress than thesecond film stress by a measurable degree is deposited, if the leaningangle is greater than the target range; or (c) with changes wherein, asthe first conformal pattern-transfer film in step (ii), a conformalpattern-transfer film having lower compressive stress than the firstfilm stress by a measurable degree is deposited, and/or, as the secondconformal pattern-transfer film in step (ii), a conformalpattern-transfer film having lower tensile stress than the second filmstress by a measurable degree is deposited, if the leaning angle issmaller than the target range; and (vii) repeating steps (v) and (vi)after increasing the measurable degree used in (b) or (c), if (b) or (c)in step (vi) is conducted. Through these steps, the vertical spacerhaving a desired or target leaning angle can effectively be formed.

In some embodiments, the first conformal pattern-transfer film has afirst resistance to dry etching, and the second conformalpattern-transfer film has a second resistance to dry etching; and step(v) further comprises judging whether a top of the vertical spacer issubstantially flat, wherein if the top of the vertical spacer is notsubstantially flat: in step (vi), as the first conformalpattern-transfer film, a first conformal pattern-transfer film which hasless resistance to dry etching than the first resistance to dry etchingand also than the second conformal pattern-transfer film by a measurabledegree is deposited, and/or, as the second conformal pattern-transferfilm, a second conformal pattern-transfer film which has higherresistance to dry etching than the second resistance to dry etching andalso than the first conformal pattern-transfer film by a measurabledegree is deposited; and in step (vii), steps (v) and (vi) are repeatedafter increasing the measurable degree, until the top of the verticalspacer is substantially flat. Accordingly, the vertical spacer havingnot only a desired leaning angle but also a substantially flat top caneffectively be formed.

In this disclosure, a “substantially flat” top of a spacer may refer toa top where a height of a top curved or slanted portion is approximately10 nm or less or alternatively or additionally is less than 20%(preferably 10% or less) of a height of the spacer (see FIG. 11).

In yet another aspect, some embodiments are directed to a method offorming spacers for spacer-defined patterning in steps comprising (i)depositing a pattern-transfer film on a template having a surfacepatterned by a mandrel formed on an underlying layer, (ii) dry-etchingthe template whose entire upper surface is covered with thepattern-transfer film, and thereby selectively removing a top portion ofthe pattern-transfer film formed on a top of the mandrel and ahorizontal portion of the pattern-transfer film formed on the underlyinglayer while leaving the mandrel as a core material and sidewall portionsof the pattern-transfer film formed on sidewalls of the mandrel asspacers, and (iii) dry-etching the core material, forming a vacantspace, whereby the template has a surface patterned by the spacers onthe underlying layer, wherein a shoulder part of each spacer facing thevacant space, which shoulder part is an outer corner of a top of thespacer, is lost or etched, forming an inclined surface from an outerside to an inner side of the top of the spacer.

In the above, the improvement comprises: in step (i), depositing, as thepattern-transfer film, a conformal pattern-transfer film constituted bya two-layer film including a first layer and a second layer deposited onthe first layer wherein the first layer has less resistance to dryetching than does the second layer, wherein a difference in resistanceto dry etching between the first layer and the second layer is such thatin step (iii), the top of each spacer becomes substantially flat byinhibiting shoulder loss of the spacer by dry etching. Accordingly, thespacer having a substantially flat top can effectively be formed.

In some embodiments, the first layer is constituted by silicon nitride,and the second layer is constituted by silicon oxide.

Embodiments will be explained with respect to the drawings. However, thepresent invention is not limited to the drawings.

FIG. 2 is a flowchart illustrating steps of fabricating a verticalspacer structure according to an embodiment of the present invention. Instep (i), a template having a surface patterned by a mandrel formed onan underlying layer is provided in a reaction space. The pattern by themandrel can be formed by photolithography using conventional UV light orextreme UV light. The mandrel is made of an organic photoresistmaterial.

In step (ii), a first conformal pattern-transfer film having a firstfilm stress is deposited, and continuously a second conformalpattern-transfer film having a second film stress is deposited on theentire patterned surface of the template, wherein the first and secondfilm stresses are different. Typically, the conformal pattern-transferfilm is formed by ALD such as PEALD, thermal ALD, or any equivalentdeposition method.

In step (iii), the template whose entire upper surface is covered withthe first and second pattern-transfer films is dry-etched, therebyselectively removing a portion of the first and second pattern-transferfilms formed on a top of the mandrel and a horizontal portion of thefirst and second pattern-transfer films while leaving the mandrel as acore material and a vertical portion of the first and secondpattern-transfer films as vertical spacers. This step is also referredto as etchback. The dry etching is typically performed using a plasmausing a suitable etchant gas which is selected for the composition ormaterial of the target film. Preferably, plasma etching uses acapacitively coupled plasma or a direct plasma, since such plasmacontains ions in addition to radicals, whereas a remote plasma hassubstantially no ions. Further, such plasma is typically anisotropic andis suitable for patterning.

In step (iv), the core material is dry-etched, forming a vacant spacebetween the vertical spacers, whereby the template has a surfacepatterned by the vertical spacers on the underlying layer. This step isalso referred to as ashing or stripping. An etchant gas is selected forthe composition or material to be removed.

FIG. 3 is a flowchart illustrating steps of adjusting the shape of avertical spacer structure according to another embodiment of the presentinvention, which can be conducted when the film profile obtainedaccording to the flowchart illustrated in FIG. 2 is not satisfactory,typically in terms of the vertical degree of the spacer. In step (v), aleaning angle of the vertical spacer is measured, followed by judgingwhether the leaning angle is within a target range in step D1. FIG. 7illustrates a leaning angle. FIG. 7 is a STEM (Scanning TransmissionElectron Microscope) photograph of a cross sectional view of spacersfabricated on a substrate according to an embodiment of the presentinvention, which photograph is annotated to show a leaning angle. Asillustrated in FIG. 7, the leaning angle θ is defined as an angle of aninner face 104 a of a vertical spacer 104 facing a vacant space 110 asmeasured with reference to a line vertical to a bottom face 102 a of abottom 102 of the vacant space 110 wherein a leaning angle of zerorepresents completely vertical and a leaning angle θ of a positive valuerepresents leaning inward, whereas a leaning angle θ of a negative valuerepresents leaning outward.

In step D1, it is judged whether the leaning angle is within a targetrange. If the leaning angle is judged to be within the target range, instep (vi)(a), steps (i) to (iv) are conducted again without changes toform final vertical spacers, i.e., the process ends.

In step D1, if the leaning angle is judged not to fall within the targetrange and to be greater than the target range, in step (vi)(b), steps(i) to (iv) are conducted again with changes wherein, as the firstconformal pattern-transfer film in step (ii), a conformalpattern-transfer film having higher compressive stress than the firstfilm stress by a measurable degree is deposited, and/or, as the secondconformal pattern-transfer film in step (ii), a conformalpattern-transfer film having higher tensile stress than the second filmstress by a measurable degree is deposited.

In step D1, if the leaning angle is judged not to fall within the targetrange and to be smaller than the target range, in step (vi)(c), steps(i) to (iv) are conducted again with changes wherein, as the firstconformal pattern-transfer film in step (ii), a conformalpattern-transfer film having lower compressive stress than the firstfilm stress by a measurable degree is deposited, and/or, as the secondconformal pattern-transfer film in step (ii), a conformalpattern-transfer film having lower tensile stress than the second filmstress by a measurable degree is deposited, if the leaning angle issmaller than the preset range.

In a step subsequent to step (vi)(b) or step (vi)(c), the process goesback to steps (v) and (vi) after increasing the measurable degree usedin step (vi)(b) or step (vi)(c).

Step D2 and step (vii) are additional or optional steps which enable thetop of the spacer to be substantially flat (the additional, optional, oralternative flow is indicated with broken lines). In step D2, it isjudged whether a top of the vertical spacer is substantially flat. Ifthe top of the vertical spacer is judged not to be substantially flat,in step (vii), as the first conformal pattern-transfer film, a firstconformal pattern-transfer film which has less resistance to dry etchingthan the first resistance to dry etching and also than the secondconformal pattern-transfer film by a measurable degree is deposited,and/or, as the second conformal pattern-transfer film, a secondconformal pattern-transfer film which has higher resistance to dryetching than the second resistance to dry etching and also than thefirst conformal pattern-transfer film by a measurable degree isdeposited, and the process moves to step (vi)(b) or step (vi)(c) afterincreasing the measurable degree so as to not only adjust the leaningangle but also the top profile of the vertical spacer.

Adjusting the top profile of the vertical spacer can be conductedindependently of adjusting the leaning angle of the vertical spacer insome embodiments. FIG. 15 is a flowchart illustrating steps of adjustingthe top profile of a vertical spacer structure according to anotherembodiment of the present invention. In step (1), the top profile of thevertical spacer is evaluated. In step (2), it is judged whether the topof the spacer is substantially flat. If the top of the spacer is judgedto be substantially flat, in step (3), the process goes back to steps(i) to (iv) illustrated in the flowchart of FIG. 2 without changes tothe pattern-transfer film so as to form final vertical spacers. If thetop of the spacer is judged not to be substantially flat, in step (4),as the first pattern-transfer film, a pattern-transfer film having ahigher dry etch rate (DER) than the first pattern-transfer film isprepared, and/or as the second pattern-transfer film, a pattern-transferfilm having a lower DER than the second pattern-transfer film isprepared. In step (5), the process goes back to steps (i) to (iv)illustrated in the flowchart of FIG. 2 to form the revisedpattern-transfer film, and then, the process goes back to step (1).

In accordance with the flowcharts discussed above, vertical spacers canbe formed as illustrated in FIGS. 5 and 6 in spacer-defined doublepatterning (SDDP). FIG. 5 is a schematic representation of doublepatterning (steps (a) to (c)) according to an embodiment of the presentinvention. In step (a), mandrels (photoresist) 101 are patterned as acore material on an underlying layer 102. In step (b), apattern-transfer film 105 comprised of a first layer 105 a and a secondlayer 105 b is deposited to cover the exposed surfaces of the mandrels101 and the exposed surface of the underlying surface 102 in theirentirety. In step (c), by dry etching, the horizontal portions of thefilm 105 and the mandrels 101 are etched so as to form spacers 106constituted by an inner layer 106 a (the first layer 105 a) and an outerlayer 106 b (the second layer 105 b). By using the above process, apattern constituted by the spacers 106 in step (c) can have a pitchwhich is a half of that of the pattern of the photoresist 101 in step(a), i.e., double-dense pitched patterning can be accomplished. In thisprocess, as discussed in this disclosure, since the spacers 106 areformed from the two-layer pattern-transfer film 105, the leaning angleof the spacers can be adjusted by using the difference in film stressbetween the first and second layers, thereby forming spacers having aleaning angle of substantially zero (not leaning toward a vacant space110 during and after the core-stripping step (c) as shown in FIG. 4).The leaning phenomenon can effectively be inhibited so as to make iteasy for semiconductor manufacturers to continuously conduct subsequentintegration processes precisely. It is expected that the above featurewill become more important as technology advances and miniaturizationprogresses.

FIG. 6 is a schematic representation of double patterning (steps (a) to(c)) according to another embodiment of the present invention. In step(a), mandrels (photoresist) 101 are patterned as a core material on anunderlying layer 102. In step (b), a pattern-transfer film 107 comprisedof a first layer 107 a and a second layer 107 b is deposited to coverthe exposed surfaces of the mandrels 101 and the exposed surface of theunderlying surface 102 in their entirety. The first layer 107 a has ahigher dry etch rate than does the second layer 107 b. In step (c), bydry etching, the horizontal portions of the film 107 and the mandrels101 are etched so as to form spacers 108 constituted by an inner layer108 a (the first layer 107 a) and an outer layer 108 b (the second layer107 b). By using the above process, a pattern constituted by the spacers106 in step (c) can have a pitch which is a half of that of the patternof the photoresist 101 in step (a), i.e., double-dense pitchedpatterning can be accomplished. In this process, as discussed in thisdisclosure, since the spacers 108 are formed from the two-layerpattern-transfer film 107, a top profile 112 of the spacers can beadjusted by using the difference in dry etch rate between the first andsecond layers, thereby making a top portion 112 of the spacers becomesubstantially flat (inhibiting shoulder loss as shown in FIGS. 4 and 5).The shoulder loss phenomenon can effectively be inhibited so as to makeit easy for semiconductor manufacturers to continuously conductsubsequent integration processes precisely. It is expected that theabove feature will become more important as technology advances andminiaturization progresses.

In the spacer illustrated in FIG. 6, since the top edge of the two-layerspacer is substantially flat, the spacer can effectively and suitably beapplied to not only SDDP but also spacer-defined quadruple patterning(SDQP) or a higher level (spacer-defined multiple patterning, SDMP), byusing the spacers 108 as the mandrels 101 in step (a) in FIG. 6, andrepeating steps (b) and (c).

Without intending to limit the present invention, the flatteningmechanism may be explained as illustrated in FIG. 12. FIG. 12illustrates the mechanism of forming a spacer having a flat top wherein(a) schematically illustrates a two-layer film used for forming thespacer, and (b) to (f) are enlarged schematic partial views showingsteps according to an embodiment of the present invention. Prior toetching, a mandrel 101 formed on a substrate 102 is covered with a firstlayer (inner layer) 107 a of a pattern-transfer film 107, which iscovered with a second layer (outer layer) 107 b of the pattern-transferfilm 107 as illustrated in (a). The inner layer 107 a is constituted bysilicon nitride, whereas the outer layer 107 b is constituted by siliconoxide in this example, wherein the inner layer 107 a has a dry etch ratewhich is higher than that of the outer layer 107 b. The sidewall portionof the pattern-transfer film 107 will form a spacer as illustrated in(b) which is an enlarged view of an upper sidewall portion (shoulderpart) 60 of the pattern-transfer film 107. First, the outer layer 107 bat the shoulder part is predominantly etched anisotropically by a plasmacontaining ions, thereby exposing the inner layer 107 a at the shoulderpart wherein an etched surface 107 a 1 of the inner layer 107 a and anetched surface 107 b 1 of the outer layer 107 b are exposed asillustrated in (c). Since the shoulder part 60 is rounded, the exposedsurfaces formed by anisotropic etching are naturally inclined asillustrated in (c). As anisotropic etching progresses (etchingconditions are switched from those set mainly for etching siliconnitride to those set mainly for etching silicon oxide in this example),the exposed surface 107 a 1 of the inner layer 107 a is etched more thanis the exposed surface 107 b 1 of the outer layer 107 b by ionbombardment or ion irradiation from the plasma since the inner layer 107a has a higher dry etch rate than does the outer layer 107 b, therebyforming an exposed surface 107 a 2 of the inner layer 107 a and anexposed surface 107 b 2 and an exposed surface 107 b 3 of the outerlayer 107 b as illustrated in (d). The exposed surface 107 b 3 of theouter layer 107 b is formed due to the difference in etching speedbetween the inner layer 107 a and the outer layer 107 b, wherein theinner layer 107 a is etched faster than is the outer layer 107 b,thereby forming a step (tapered protrusion) between the inner layer 107a and the outer layer 107 b. Since the exposed surface 107 a 2 isinclined and ion bombardment is reflected on the exposed surface 107 a 2toward the exposed surface 107 b 3 (as illustrated by arrows in (d)),the exposed surface 107 b 3 receives the reflected ions, and the taperedprotrusion is etched from its tip by the reflected ions. As anisotropicetching further progresses, ions reflected by an exposed surface 107 a 3keep bombarding the tapered protrusion, thereby lowering the height ofthe tapered protrusion as illustrated in (e), wherein a portion 107 b 5indicated by a broken line is removed, thereby forming an exposedsurface 107 b 4. As anisotropic etching further progresses, the heightof the protrusion is lowered, and an exposed surface 107 a 4 and anexposed surface 107 b 6 lead to formation of a substantially flatsurface as illustrated in (f).

The two-layer film disclosed herein can be used in various applications,including spacer-defined double patterning (SDDP). FIG. 14 is aschematic representation of pattern transfer and target etching usingSDDP according to an embodiment of the present invention, wherein atwo-layer film is used as a pattern-transfer film to transfer a patternfrom a first template to a second template. An antireflective layer(ARL) 94 is used as the first template for increasing pattern density(e.g., pitch reduction) in SDDP processes. An etch hardmask 82 is usedas the second template for etching a target layer 81. In step (a) inFIG. 14, on the antireflective layer 94 (constituted by e.g., amorphouscarbon), a photoresist pattern 93 (constituted by e.g., Novolacs) isformed so that the antireflective layer 94 can be etched in thephotoresist pattern in step (b) which is a step of transferring apattern to the first template 94. In step (c), a two-layer film 95 (as apattern-transfer film) is deposited according to any of the disclosedembodiments or equivalents thereto, followed by etching in step (d)which is a spacer RIE (reactive ion etch) step. By stripping thematerial of the antireflective layer 94 (a photoresist material in thecore portions 96), vertical spacers 84 are formed in step (e). Since thetwo-layer film 95 has high etch selectivity, the antireflective layer 94(the first template) for forming the spacer thereon can be thin and thetwo-layer film can be preserved during etching to form the verticalspacers 84 in step (e). In some embodiments, the thickness of theantireflective layer is about 5 to 50 nm (typically 10 to 30 nm), andthe thickness of the two-layer film is about 5 to 50 nm (typically 10 to20 nm). In step (f), the pattern is transferred by etching from thevertical spacers 84 to the second template 82 to form second verticalspacers 74, and in step (g), the first vertical spacers 84 (two-layerspacers) are stripped. Since the top edge of the two-layer spacer 84 isflat, formation of the second template 82 with the second verticalspacers 74 can be accurately accomplished. In step (h), a target layer81 formed on a silicon substrate 70 is subjected to dry etch using thesecond vertical spacers 74. In step (i), the second vertical spacers 74are stripped. In some embodiments, the antireflective layer, etchhardmask, two-layer film (spacer), and target layer may be deposited byany of the methods disclosed herein or equivalents thereof or by pulsedPECVD or PEALD.

The two-layer film is resistant to not only HCl, and TMAH wet etch, butalso e.g. to BCl₃, BCl₃/Ar, dry etch, and thus, in step (f), whentransferring the pattern to the second template 82, the two-layer 84preserves the pattern. On the other hand, the two-layer film issensitive to oxidation, a combination of wet etch chemistry alternatingoxidizing and HF (common in semiconductor processing), or dry etch basedon oxygen or CF₄, for example, and thus, in step (g), the two-layerspacer 84 can effectively be stripped.

The pattern-transfer film having a different film stress can be formedby manipulating deposition parameters such as RF power, the duration ofRF power pulse, the flow rate of reactant, the number of additionallyconducted sub-cycles or reforming cycles, etc. A skilled artisan canreadily determine such deposition parameters as a matter of routineexperimentation in view of this disclosure.

As for a silicon oxide film used as a first and/or second layer(s) of apattern-transfer film, for example, by manipulating feed of reactant,the film stress of a resultant silicon oxide film can be adjusted. FIG.16 illustrates a process sequence in one cycle of deposition of asilicon oxide film having a different film stress according to anembodiment of the present invention, wherein the one cycle isconstituted by cycle A and cycle B. In this embodiment, cycle A is aprimary cycle whereas cycle B is a sub-cycle (secondary cycle). Bothcycles are comprised of “Feed” where a Si precursor is fed to a reactionspace so that the precursor is adsorbed or chemisorbed on a surface of atemplate, “Purge” where the reaction space is purged so that excessprecursor which is not adsorbed or chemisorbed is removed from thesurface of the template, “RF” where RF power is applied to the reactionspace so that adsorbed or chemisorbed precursor is exposed to a plasmato form an atomic layer, and “Purge” where the reaction space is purgedso that non-reacted components and byproducts are removed from thesurface of the template. The precursor is supplied to the reaction spaceusing a flow of carrier gas which is constantly and continuouslysupplied to the reaction space throughout the cycle. In cycle A, oxygenis constantly and continuously supplied to the reaction space throughoutcycle A (so as to generate an oxygen-argon plasma), whereas in cycle B,no oxygen is supplied to the reaction space throughout cycle B (so as togenerate an argon plasma). Further, RF power in cycle B may be higherthan that in cycle A, and/or the duration of RF power pulse in cycle Bmay be longer than that in cycle A. Cycle B is conducted n times (n isan integer of 0 to 10, e.g., 1 to 5) after cycle A is conducted once. Bychanging the number of repetitions (n) of cycle B, the film stress ofresultant silicon oxide film can be changed in a compressive direction.Additionally or alternatively, by changing RF power and/or the durationof RF power pulse in cycle A, the film stress of silicon oxide film canalso be adjusted. In some embodiments, the film stress of silicon oxidefilm can be changed in a range of approximately +100 MPa toapproximately −300 MPa, preferably approximately 0 MPa to approximately−200 MPa.

The dry etch rate of silicon oxide can be adjusted by changing a ratioof flow rate of reactant gas and flow rate of dilution gas, for example.In some embodiments, the dry etch rate of silicon oxide can be changedin a range of approximately 0.7 nm/sec. to approximately 1.5 nm/sec.,preferably approximately 0.5 nm/sec. to approximately 1.0 nm/sec,depending on the dry etching conditions.

For deposition of a silicon oxide film, as a precursor, BDEAS(bisdiethylaminosilane), 3DMAS (tris(dimethylamino)silane), or the likecan be favorably used singly or in any combination of two or more of theforegoing. As each of a carrier gas and a dilution gas, Ar, He, or thelike can be favorably used singly or in any combination of two or moreof the foregoing. As a reactant gas, O₂, N₂O, or the like can befavorably used singly or in any combination of two or more of theforegoing.

In some embodiments, the deposition cycle of silicon oxide film may beperformed by PEALD using the process sequence illustrated in FIG. 16,one cycle of which is conducted under conditions shown in Table 1 below.

TABLE 1 (numbers are approximate) Conditions for Deposition Cycle ofSilicon Oxide Film Cycle A Substrate temperature 75 to 200° C.(preferably 90 to 120° C.) Pressure 300 to 800 Pa (preferably 350 to 450Pa) Precursor pulse (“Feed 1”) 0.5 to 2.0 sec (preferably 0.5 to 1.0sec) Precursor purge (“Purge 1”) 1.5 to 4.0 sec (preferably 2.0 to 3.0sec) Flow rate of reactant (continuous) 1.0 to 4.0 sccm (preferably 1.5to 2.5 sccm) Flow rate of carrier gas 1.0 to 4.0 sccm (preferably 1.5 to2.5 sccm) (continuous) Flow rate of dilution gas 1.0 to 4.0 sccm(preferably 1.5 to 2.5 sccm) (continuous) RF power (13.56 MHz) for a300-mm 30 to 300 W (preferably 50 to 100 W) wafer RF power pulse (“RF1”) 0.1 to 2.0 sec (preferably 0.2 to 1.0 sec) Purge (“Purge 2”) 0.1 to0.5 sec (preferably 0.1 to 0.2 sec) Growth rate per cycle (on top 0.1 to0.5 nm/cycle surface) Distance between electrodes 9.0 to 15.0 mm(preferably 10.0 to 12.0 mm) Cycle B Substrate temperature 75 to 200° C.(preferably 90 to 120° C.) Pressure 300 to 800 Pa (preferably 350 to 450Pa) Precursor pulse (“Feed 2”) 0.5 to 2.0 sec (preferably 0.5 to 1.0sec) Precursor purge (“Purge 3”) 1.5 to 4.0 sec (preferably 2.0 to 3.0sec) Flow rate of carrier gas 1.0 to 4.0 sccm (preferably 1.5 to 2.5sccm) (continuous) Flow rate of dilution gas 2.0 to 8.0 sccm (preferably3.0 to 6.0 sccm) (continuous) RF power (13.56 MHz) for a 300-mm 100 to500 W (preferably 200 to 300 W) wafer RF power pulse (“RF 2”) 1.0 to 4.0sec (preferably 1.5 to 2.5 sec) Purge (“Purge 4”) 0.5 to 2.0 sec(preferably 0.5 to 1.0 sec) Growth rate per cycle (on top 0.0 to 0.05nm/cycle surface) Distance between electrodes 9.0 to 15.0 mm (preferably10.0 to 12.0 mm) Step coverage (side/top) 90 to 100% (preferably 95 to100%) Cycle ratio (n = cycle B/cycle A) 0 to 5 (preferably 0 to 3)

In the above, for other sizes of substrate, the wattage per cm²calculated from the above can be applied.

As for a silicon nitride film used as a first and/or second layer(s) ofa pattern-transfer film, for example, by manipulating feed of reactant,the film stress of a resultant silicon nitride film can be adjusted.FIG. 17 illustrates a process sequence in one cycle of deposition of asilicon nitride film having a different film stress according to anembodiment of the present invention. In this embodiment, the cycle iscomprised of “Feed” where a Si precursor is fed to a reaction space sothat the precursor is adsorbed or chemisorbed on a surface of atemplate, “Purge 1” where the reaction space is purged so that excessprecursor which is not adsorbed or chemisorbed is removed from thesurface of the template, “RF” where RF power is applied to the reactionspace so that adsorbed or chemisorbed precursor is exposed to a plasmato form an atomic layer, and “Purge 2” where the reaction space ispurged so that non-reacted components and byproducts are removed fromthe surface of the template. The precursor is supplied to the reactionspace using a flow of carrier gas which is constantly and continuouslysupplied to the reaction space throughout the cycle. In the cycle, Arand N₂ are constantly and continuously supplied to the reaction spacethroughout the cycle. By changing RF power and/or the duration of RFpower pulse in the cycle, the film stress of silicon nitride film can beadjusted. For example, by increasing the duration of RF power pulse, thefilm stress of silicon nitride can be changed in a compressivedirection. In some embodiments, the film stress of silicon nitride filmcan be changed in a range of approximately −300 MPa to approximately−900 MPa, preferably approximately −400 MPa to approximately −800 MPa.

The dry etch rate of silicon nitride can be adjusted by the duration ofRF power pulse in the cycle. In some embodiments, the dry etch rate ofsilicon nitride can be changed in a range of approximately 0.5 nm/sec.to approximately 2 nm/sec., preferably approximately 1 nm/sec. toapproximately 1.5 nm/sec, depending on the dry etching conditions.

For deposition of a silicon nitride film, as a precursor, BDEAS(bisdiethylaminosilane), DCS (dichlorosilane), silane, or the like canbe favorably used singly or in any combination of two or more of theforegoing. As each of a carrier gas and a dilution gas, Ar, He, or thelike can be favorably used singly or in any combination of two or moreof the foregoing. A dilution gas need not be used and can be entirelyeliminated (as in Example 1 discussed below). As a reactant gas, N₂, H₂,NH₃, or the like can be favorably used singly or in any combination oftwo or more of the foregoing.

In some embodiments, the deposition cycle of silicon nitride film may beperformed by PEALD using the process sequence illustrated in FIG. 17,one cycle of which is conducted under conditions shown in Table 2 below.

TABLE 2 (numbers are approximate) Conditions for Deposition Cycle ofSilicon Nitride Film Substrate temperature 75 to 200° C. (preferably 100to 180° C.) Pressure 150 to 3000 Pa (preferably 300 to 500 Pa) Precursorpulse (“Feed”) 0.1 to 1.0 sec (preferably 0.3 to 0.45 sec) Precursorpurge (“Purge 1”) 0.1 to 2.0 sec (preferably 0.5 to 1.0 sec) Flow rateof reactant (continuous) 1000 to 15000 sccm (preferably 2500 to 10000sccm) Flow rate of carrier gas (continuous) 500 to 4000 sccm (preferably1000 to 2000 sccm) Flow rate of dilution gas (continuous) 0 to 15000sccm (preferably 0 to 10000 sccm) RF power (13.56 MHz) for a 300-mm 100to 500 W (preferably 200 to 300 W) wafer RF power pulse (“RF”) 1 to 5sec (preferably 2 to 4 sec) Purge (“Purge 2”) 0 to 1 sec (preferably 0.1to 0.2 sec) Growth rate per cycle (on top surface) 0.01 to 0.1 nm/cycleStep coverage (side/top) 80 to 100% (preferably 90 to 100%) Distancebetween electrodes 7.5 to 20 mm (preferably 10 to 15 mm)

In the above, for other sizes of substrate, the wattage per cm²calculated from the above can be applied.

In some embodiments, silicon nitride film can be deposited using themethod disclosed in U.S. Patent Publication No. 2017/0062204 A1,particularly FIGS. 4A and 4B and the corresponding text of thepublication, the disclosure of which is herein incorporated by referencein its entirety.

In some embodiments, dry etching of the silicon oxide film (etchbackprocess) is conducted under the conditions shown in Table 3 below.

TABLE 3 (numbers are approximate) Conditions for Dry Etching (Etchback)of Silicon Oxide Thickness of SiO film to be 5 to 40 nm (preferably 10to 20 nm) etched Substrate temperature 20 to 100° C. (preferably 40 to60° C.) Pressure 3 to 10 Pa (preferably 4 to 8 Pa) Etchant gas CF₄,CHF₃, C₄F₈ Flow rate of etchant gas 10 to 100 sccm (preferably 20 to 40sccm) (continuous) Flow rate of dilution gas 100 to 300 sccm (preferably150 to 250 sccm); (continuous) He, Ar High RF power (13.56 or 27.12 MHz)100 to 1000 W (preferably 300 to 500 W) for a 300-mm wafer Low RF power(400 kHz) for a 50 to 500 W (preferably 100 to 300 W) 300-mm waferDuration of RF power 5 to 40 sec. (preferably 10 to 20 sec.) applicationDistance between electrodes 20 to 60 mm (preferably 30 to 40 mm) Etchrate 0.5 to 5 nm/sec. (preferably 0.8 to 2 nm/sec.)

In the above, for other sizes of substrate, the wattage per cm²calculated from the above can be applied.

In some embodiments, dry etching of the SiN film (etchback process) isconducted under the conditions shown in Table 4 below.

TABLE 4 (numbers are approximate) Conditions for Dry Etching (Etchback)of Silicon Nitride Thickness of SiN film to be 5 to 40 nm (preferably 10to 20 nm) etched Substrate temperature 20 to 100° C. (preferably 40 to60° C.) Pressure 3 to 10 Pa (preferably 4 to 8 Pa) Etchant gas CF₄,CHF₃, C₄F₈ Flow rate of etchant gas 10 to 100 sccm (preferably 20 to 40sccm) (continuous) Flow rate of dilution gas 100 to 300 sccm (preferably150 to (continuous) 250 sccm); He, Ar Secondary etchant gas O₂ (10 to100 sccm, preferably 20 to (continuous) 40 sccm) High RF power 100 to1000 W (preferably 300 to 500 W) (13.56 or 27.12 MHz) for a 300-mm waferDuration of RF power 5 to 40 sec. (preferably 10 to 20 sec.) applicationDistance between 20 to 60 mm (preferably 40 to 45 mm) electrodes Etchrate 0.5 to 5 nm/sec. (preferably 0.8 to 2 nm/sec.)

In the above, for other sizes of substrate, the wattage per cm²calculated from the above can be applied.

The first layer and the second layer of the pattern-transfer film can beconstituted by different compositions or same compositions as long asthe difference in film stress between the first and second layers isproperly adjusted (e.g., a difference of approximately 150 MPa toapproximately 800 MPa, preferably approximately 200 MPa to approximately600 MPa, depending also on the thickness of each layer wherein adifference in a product of the film stress and the thickness of eachlayer is considered), and additionally or alternatively, as long as thedifference in dry etch rate between the first and second layers isproperly adjusted (e.g., a difference of approximately 0.1 nm/sec. toapproximately 2 nm/sec., preferably approximately 0.2 nm/sec. toapproximately 1.5 nm/sec., depending also on the common etchingconditions). For example, the following combinations (the first/secondlayers) can favorably be selected: SiN/SiO, SiO/SiN, SiO/SiO, andSiN/SiN. When the first (inner) layer is SiN and the second (outer)layer is SiO, SiO is first etched under etching conditions set for SiO,and then SiN is etched under etching conditions set for SiN on a topportion of the mandrel during the etchback step. The etching conditionsare switched from those for SiO to those for SiN (i) when a portion ofthe SiO layer at the top portion of the mandrel becomes thin or isalmost exposed, (ii) when a part or most of the SiO layer at the topportion of the mandrel (except for a top portion of the sidewall of theSiO layer) is removed and the SiN film is exposed at the top portion ofthe mandrel, or (iii) at the timing between (i) and (ii) above. When thedry etch rate of the SiN layer is higher than that of the SiO layerunder the etching conditions set for SiN, flattening effect illustratedin FIG. 12 can be achieved.

In some embodiments, dry etching of the core material (ashing orstripping process) is conducted under the conditions shown in Table 5below.

TABLE 5 (numbers are approximate) Conditions for Dry Etching(Ashing/stripping) of Core Material Substrate temperature 20 to 100° C.(preferably 40 to 60° C.) Pressure 3 to 40 Pa (preferably 8 to 30 Pa)Etchant gas O₂ Flow rate of etchant gas 10 to 1000 sccm (preferably 20to 400 sccm) (continuous) Flow rate of dilution gas 0 to 1000 sccm(preferably 0 to 400 sccm); (continuous) He, Ar High RF power 100 to2000 W (preferably 300 to 500 W) (13.56 or 27.12 MHz) for a 300-mm waferDuration of RF power 10 to 60 sec. (preferably 20 to 45 sec.)application Distance between 20 to 60 mm (preferably 40 to 45 mm)electrodes

In the above, for other sizes of substrate, the wattage per cm²calculated from the above can be applied.

The deposition process, etchback process, and ashing process can beperformed in a same reaction chamber or different reaction chambers.When different reaction chambers are used, preferably, the chambers areconnected via a wafer-handling chamber with a vacuum robot so thatexposure of substrates to air can be avoided, and throughput can beincreased.

The process cycle can be performed using any suitable apparatusincluding an apparatus illustrated in FIG. 1, for example. FIG. 1 is aschematic view of a PEALD apparatus, desirably in conjunction withcontrols programmed to conduct the sequences described below, usable insome embodiments of the present invention. In this figure, by providinga pair of electrically conductive flat-plate electrodes (capacitivelycoupled electrodes) 4, 2 in parallel and facing each other in theinterior 11 (reaction zone) of a reaction chamber 3, applying HRF power(13.56 MHz or 27 MHz) 20 to one side, and electrically grounding theother side 12, a plasma is excited between the electrodes. A temperatureregulator is provided in a lower stage 2 (the lower electrode), and atemperature of a substrate 1 placed thereon is kept constant at a giventemperature. The upper electrode 4 serves as a shower plate as well, andreactant gas (and noble gas) and precursor gas are introduced into thereaction chamber 3 through a gas line 21 and a gas line 22,respectively, and through the shower plate 4. Additionally, in thereaction chamber 3, a circular duct 13 with an exhaust line 7 isprovided, through which gas in the interior 11 of the reaction chamber 3is exhausted. Additionally, a dilution gas is introduced into thereaction chamber 3 through a gas line 23. Further, a transfer chamber 5disposed below the reaction chamber 3 is provided with a seal gas line24 to introduce seal gas into the interior 11 of the reaction chamber 3via the interior 16 (transfer zone) of the transfer chamber 5 wherein aseparation plate 14 for separating the reaction zone and the transferzone is provided (a gate valve through which a wafer is transferred intoor from the transfer chamber 5 is omitted from this figure). Thetransfer chamber is also provided with an exhaust line 6. In someembodiments, the deposition of multi-element film and surface treatmentare performed in the same reaction space, so that all the steps cancontinuously be conducted without exposing the substrate to air or otheroxygen-containing atmosphere. In some embodiments, a remote plasma unitcan be used for exciting a gas. In some embodiments, the system ofswitching flow of an inactive gas and flow of a precursor gas can beused to introduce the precursor gas in pulses without substantiallyfluctuating pressure of the reaction chamber.

In some embodiments, a dual-chamber reactor (two sections orcompartments for processing wafers disposed close to each other) can beused, wherein a reactant gas and a noble gas can be supplied through ashared line whereas a precursor gas is supplied through unshared lines.

A skilled artisan will appreciate that the apparatus includes one ormore controller(s) (not shown) programmed or otherwise configured tocause the deposition and reactor cleaning processes described elsewhereherein to be conducted. The controller(s) are communicated with thevarious power sources, heating systems, pumps, robotics, and gas flowcontrollers or valves of the reactor, as will be appreciated by theskilled artisan.

The present invention is further explained with reference to workingexamples below. However, the examples are not intended to limit thepresent invention. In the examples where conditions and/or structuresare not specified, the skilled artisan in the art can readily providesuch conditions and/or structures, in view of the present disclosure, asa matter of routine experimentation. Also, the numbers applied in thespecific examples can be modified by a range of at least ±50% in someembodiments, and the numbers are approximate.

EXAMPLES Reference Example 1

SiO films and SiN films were each deposited on a Si substrate (Φ300 mm)by PEALD, one cycle of which was conducted under the conditions shown inTables 6 and 7 (deposition cycle) below using the PEALD apparatusillustrated in FIG. 1 based on the process sequence illustrated in FIGS.16 and 17.

After taking out each substrate from the reaction chamber, film stressof each film was measured. The results are shown in Table 8 below. Thefilm stress was measured based on a “warp” of the substrate before andafter the film was deposited on the substrate, wherein the “warp” wasexpressed by a radius of curvature, and the film stress was calculatedusing the Stoney equation.

TABLE 6 (numbers are approximate) Conditions for Deposition Cycle ofSilicon Oxide Film Cycle A Substrate temperature 100° C. Pressure 400 PaPrecursor BDEAS (bisdiethylaminosilane) Precursor pulse (“Feed 1”) 0.8sec Precursor purge (“Purge 1”) 2.0 sec Flow rate of oxygen (continuous)2 slm Flow rate of Ar (continuous) 2 slm RF power (13.56 MHz) for a300-mm wafer 50 W RF power pulse (“RF 1”) 0.2 sec Purge (“Purge 2”) 0.1sec Growth rate per cycle (on top surface) 0.15 nm/cycle Distancebetween electrodes 12.0 mm Cycle B Substrate temperature 100° C.Pressure 400 Pa Precursor BDEAS (bisdiethylaminosilane) Precursor pulse(“Feed 2”) 0.8 sec Precursor purge (“Purge 3”) 2.0 sec Flow rate of Ar(continuous) 4 slm RF power (13.56 MHz) for a 300-mm wafer 300 W RFpower pulse (“RF 2”) 0.2 sec Purge (“Purge 4”) 0.5 sec Growth rate percycle (on top surface) 0.0 nm/cycle Distance between electrodes 12.0 mmStep coverage (side/top) 95% Cycle ratio (n = cycle B/cycle A) See Table8

TABLE 7 (numbers are approximate) Conditions for Deposition Cycle ofSilicon Nitride Film Substrate temperature 180° C. Pressure 350 PaPrecursor H₂SiI₂ Precursor pulse (“Feed”) 0.3 sec Precursor purge(“Purge 1”) 0.5 sec Flow rate of N₂ (continuous) 4600 sccm RF power(13.56 MHz) for a 300-mm wafer 248 W RF power pulse (“RF”) See Table 8Purge (“Purge 2”) 0.1 sec Growth rate per cycle (on top surface) 0.017nm/cycle Step coverage (side/top) 95% Distance between electrodes 12 mm

TABLE 8 (numbers are approximate) Film Condition Stress (7 days afterdeposition) SiO Cycle ratio: n = 0 −10.7 n = 2 −167.4 n = 3 −169.3 n = 5−167.1 SiN RF power pulse: 2 s −458.2 3.3 s −647.3   5 s −760.1

Table 8 shows a stress measured 7 days after deposition. However, thestress immediately after deposition was substantially the same as that 7days after deposition, although the stress gradually changed slightlywith time. The gradual change was insignificant and may have been causedby film's absorption of moisture. As shown in Table 8, as for the SiOfilm, by adding cycle B, the film stress became more compressive, and asfor the SiN film, by prolonging the duration of RF power pulse, the filmstress became more compressive.

Comparative Example 1

A template was prepared by forming a mandrel pattern (made of amorphouscarbon) using a patterned SiARC (Silicon-containing antireflectioncoating) on a Si substrate (Φ300 mm), wherein the patterned mandrel hada height of 90 nm, a width of 30 nm, and a pitch of 115 nm. On thetemplate, a SiO film having a thickness of 35 nm as a single-layerpattern transfer film was deposited at a conformality of 95% by PEALDunder the conditions corresponding to those for SiO (n=0) (having a filmstress of −10.7) described in Reference Example 1. (a) in FIG. 8 shows aSTEM photograph of a cross-sectional view of the SiO single-layer film.

Next, the SiO single-layer film was subjected to an etchback processunder the conditions shown in Table 9 below, followed by an ashingprocess under the conditions shown in Table 10 below, in the samechamber as in the deposition process, so as to form spacers. Note thatthe etchback process shown in Table 9 also etched the SiARC film.

TABLE 9 (numbers are approximate) Conditions for Dry Etching (Etchback)of Silicon Oxide Substrate temperature 60° C. Pressure 4 Pa Etchant gasCF₄ Flow rate of etchant gas (continuous) 20 sccm Flow rate of dilutiongas (continuous) 180 sccm; Ar (CF₄/Ar = 1/9) High RF power (27.12 MHz)300 W Low RF power (400 kHz) 300 W Duration of RF power application 32sec. Distance between electrodes 42 mm Etch rate 1.4 nm/sec.

TABLE 10 (numbers are approximate) Conditions for Dry Etching(Ashing/stripping) of Core Material Substrate temperature 60° C.Pressure 8 Pa Etchant gas O₂ Flow rate of etchant gas (continuous) 20sccm Flow rate of dilution gas (continuous) 180 sccm; Ar (e.g., O₂/Ar =1/9) High RF power (27.12 MHz) 300 W Duration of RF power application 45sec. Distance between electrodes 42 mm

(c) in FIG. 8 shows a STEM photograph of a cross-sectional view of thespacers made from the SiO single-layer film. As shown in (c) in FIG. 8,the spacers leaned toward the vacant space through the core removal,i.e., the ashing process. The leaning angle of the spacers was measuredas approximately 2.2 degrees.

Comparative Example 2

A template was prepared and a SiO film was deposited thereon in a mannersubstantially similar to that in Comparative Example 1 except that theSiO film having a thickness of 35 nm as a single-layer pattern transferfilm was deposited at a conformality of 90% by PEALD under theconditions corresponding to those for SiO (n=3) (having a film stress of−169.3) described in Reference Example 1. (b) in FIG. 8 shows a STEMphotograph of a cross-sectional view of the SiO single-layer film.

Next, the SiO single-layer film and SiARC film were subjected to anetchback process under the same conditions as in Comparative Example 1,followed by an ashing process under the same conditions as inComparative Example 1 so as to form spacers. (d) in FIG. 8 shows a STEMphotograph of a cross-sectional view of the spacers made from the SiOsingle-layer film. As shown in (d) in FIG. 8, the spacers leaned towardthe vacant space through the core removal, i.e., the ashing process. Theleaning angle of the spacers was measured as approximately 2.9 degrees.

Example 1

A template was prepared and a SiO film was deposited in a mannersubstantially similar to that in Comparative Example 1 or 2 except thatthe SiO film was deposited as a SiO two-layer pattern-transfer filmwhich was constituted by an inner SiO single-layer film having athickness of 20 nm deposited in a manner substantially similar to thatin Comparative Example 1 (SiO (n=0)), and an outer SiO single-layer filmhaving a thickness of 15 nm deposited in a manner substantially similarto that in Comparative Example 2 (SiO (n=3)). The SiO two-layerpattern-transfer film had a conformality of 90%. (c) in FIG. 9 shows aSTEM photograph of a cross-sectional view of the SiO two-layer film.That is, the inner layer having a thickness of 20 nm was the SiOsingle-layer film having a stress of −10.7 MPa (relatively tensile),whereas the outer layer having a thickness of 15 nm was the SiOsingle-layer film having a stress of −169.3 MPa (relativelycompressive).

Next, the SiO two-layer film and SiARC film were subjected to anetchback process under the same conditions as in Comparative Example 1,followed by an ashing process under the same conditions as inComparative Example 1 so as to form spacers. (d) in FIG. 9 shows a STEMphotograph of a cross-sectional view of the spacers made from the SiOtwo-layer film. As shown in (d) in FIG. 9, the spacers leaned moretoward the vacant space through the core removal, i.e., the ashingprocess, than either of the spacers in Comparative Example 1 (θ=2.2°)shown in (a) in FIG. 9 or the spacers in Comparative Example 2 shown(θ=2.9°) in (b) of FIG. 9. The leaning angle of the spacers was measuredas approximately 6.5 degrees. This synergistic effect is summarized asfollows:

2.9° (outer)+2.2° (inner)→6.5° (total)

Example 2

A template was prepared and a SiO film was deposited in a mannersubstantially similar to that in Example 1 except that the inner layerand the outer layer were switched. That is, the SiO film was depositedas a SiO two-layer pattern-transfer film which was constituted by aninner SiO single-layer film having a thickness of 20 nm deposited in amanner substantially similar to that in Comparative Example 2 (SiO(n=3)), and an outer SiO single-layer film having a thickness of 15 nmdeposited in a manner substantially similar to that in ComparativeExample 1 (SiO (n=0)). The SiO two-layer pattern-transfer film had aconformality of 95%. (e) in FIG. 9 shows a STEM photograph of across-sectional view of the SiO two-layer film. That is, the inner layerhaving a thickness of 20 nm was the SiO single-layer film having astress of −169.3 MPa (relatively compressive), whereas the outer layerhaving a thickness of 15 nm was the SiO single-layer film having astress of −10.7 MPa (relatively tensile).

Next, the SiO two-layer film and SiARC film were subjected to anetchback process under the same conditions as in Comparative Example 1,followed by an ashing process under the same conditions as inComparative Example 1 so as to form spacers. (f) in FIG. 9 shows a STEMphotograph of a cross-sectional view of the spacers made from the SiOtwo-layer film. As shown in (f) in FIG. 9, the spacers leaned lesstoward the vacant space via the core removal, i.e., the ashing process,than either of the spacers in Comparative Example 1 (θ=2.2°) shown in(a) in FIG. 9 or the spacers in Comparative Example 2 shown (θ=2.9°) in(b) of FIG. 9. The leaning angle of the spacers was measured asapproximately 0.8 degrees. This converse effect is summarized asfollows:

2.2° (outer)+2.9° (inner)→0.8° (total)

As described above in Examples 1 and 2, by manipulating the filmstresses of the inner and outer layers, spacers having a desired leaningangle can be formed.

Example 3

A template was prepared and a SiO film was deposited in a mannersubstantially similar to that in Example 1 except that the inner layerwas deposited in a manner substantially similar to that for SiO (n=2) inTable 8 in Reference Example 1, in place of that for SiO (n=3) inExample 1.

Next, the two-layer film was used as a pattern-transfer film andsubjected to an etchback process under the same conditions as inComparative Example 1, followed by an ashing process under the sameconditions as in Comparative Example 1 so as to form spacers. A STEMphotograph of a cross-sectional view of the spacers made from thetwo-layer pattern-transfer film was obtained, and the leaning angle ofthe spacers of each example was measured. FIG. 10 is a graph showing therelationship between the leaning angle and difference in film stressbetween the outer layer and inner layer of the two-layerpattern-transfer film.

Examples 4 and 5

In Example 4, a template was prepared, a SiN film having a thickness of20 nm was deposited as an inner layer of a two-layer film in a mannersubstantially similar to that for SiN (RF=3.3 s) in Table 8 in ReferenceExample 1, and a SiO film having a thickness of 15 nm was deposited asan outer layer of the two-layer film in a manner substantially similarto that for SiO (n=0) in Table 8 in Reference Example 1. The resultanttwo-layer pattern transfer film had a conformality of 100%.

In Example 5, a template was prepared and a two-layer film was deposited(a conformality of 90%) in a manner substantially similar to that inExample 4 except that the SiN thickness was 25 nm and the SiO thicknesswas 10 nm.

Next, each of the two-layer films obtained in Examples 4 and 5 was usedas a pattern-transfer film and subjected to an etchback process underthe same conditions as in Comparative Example 1 for etching the outerSiO layer except that the duration of RF power application was 14seconds for Example 4 and 10 seconds for Example 5, until a surface ofthe inner SiN layer was almost exposed. Thereafter, the etchingconditions were changed for etching the inner SiN layer as shown inTable 11 below.

TABLE 11 (numbers are approximate) Conditions for Dry Etching (Etchback)of Silicon Nitride Thickness of SiN film to be etched 20 nm Substratetemperature 60° C. Pressure 8 Pa Etchant gas CHF₃ Flow rate of etchantgas (continuous) 20 sccm Flow rate of dilution gas (continuous) 360sccm; Ar Secondary etchant gas (continuous) O₂ (20 sccm) High RF power(27.12 MHz) 300 W Duration of RF power application 18 sec. for Example 4and 19 sec for Example 5 Distance between electrodes 42 mm Etch rate 1.1nm/sec.

Thereafter, an etching process of the SiARC layer was conducted underthe conditions shown in Table 9 except that the duration of RF powerapplication was 9 sec. Thereafter, an ashing process was conducted underthe same conditions as in Comparative Example 1 so as to form spacers. ASTEM photograph of a cross-sectional view of the spacers made from eachtwo-layer pattern-transfer film was obtained, and the leaning angle ofthe spacers of each example was measured. FIG. 10 is a graph showing therelationship between the leaning angle and difference in film stressbetween the outer layer and inner layer of each two-layerpattern-transfer film.

Comparative Example 3

A template was prepared and a SiO single-layer pattern-transfer film wasdeposited in a manner substantially similar to that in ComparativeExample 1 (n=0) except that n was 2.

Next, the single-layer film was used as a pattern-transfer film andsubjected to an etchback process under the same conditions as inComparative Example 1, followed by an ashing process under the sameconditions as in Comparative Example 1 so as to form spacers. A STEMphotograph of a cross-sectional view of the spacers made from thesingle-layer pattern-transfer film was obtained, and the leaning angleof the spacers was measured. FIG. 10 is a graph showing the leaningangle of the single-layer pattern-transfer film (“C. Ex. 3”) where thedifference between an inner half and an outer half of the film waspresumed as zero.

Comparative Example 4

A template was prepared and a SiN single-layer pattern-transfer film wasdeposited in a manner substantially similar to that for SiN in ReferenceExample 1 (RF=3.3 s).

Next, the single-layer film was used as a pattern-transfer film andsubjected to an etchback process under the same conditions as inComparative Example 1, followed by an ashing process under the sameconditions as in Comparative Example 1 so as to form spacers. A STEMphotograph of a cross-sectional view of the spacers made from thesingle-layer pattern-transfer film was obtained, and the leaning angleof the spacers was measured. FIG. 10 is a graph showing the leaningangle of the single-layer pattern-transfer film (“C. Ex. 4”) where thedifference between an inner half and an outer half of the film waspresumed to be zero.

As shown in FIG. 10 (which also plots the results of Examples 1 and 2and Comparative Examples 1 and 2), the greater the difference in filmstress in a negative direction, the greater the leaning angle of thespacers becomes in a positive direction (leaning inward), whereas thegreater the difference in film stress in a positive direction, thegreater the leaning angle of the spacers becomes in a negative direction(leaning outward). Accordingly, by manipulating the film stresses of theinner and outer layers, spacers having a desired leaning angle (e.g., arange of ±2° or ±1°) can be formed.

Example 6

A template was prepared and a SiN/SiO two-layer film was formed in amanner substantially similar to that in Example 4. The resultanttwo-layer film had a conformality of 100%.

Next, the two-layer film was used as a pattern-transfer film andsubjected to an etchback process, followed by an ashing process in amanner substantially similar to those in Example 4 so as to formspacers. Under the etching conditions shown in Table 11, the dry etchrate of the SiO layer was 0.4 nm/sec. whereas that of the SiN layer was1.5 nm/sec. FIG. 11 shows STEM photographs of cross-sectional viewsannotated to show “shoulder loss” (a circled portion), wherein (a) showsthe spacers formed in Comparative Example 1, and (b) shows the spacersformed in Example 6. The shoulder loss can be evaluated based on aheight H1 of the inclined slope of a spacer 104, which was 40 nm in (a)of FIG. 11, whereas a height H2 of the inclined slope of a spacer 108(constituted by an inner SiN layer 108 a and an outer SiO layer 108 b)was 5 nm. As shown in FIG. 11, by using the two-layer pattern-transferfilm having a difference in dry etch rate between the inner and outerlayers, the top of the spacer became substantially flat. The theory ofthe flattening mechanism was considered to be that illustrated in FIG.12 described earlier.

Example 7

In this example, the flattening mechanism illustrated in FIG. 12 wasconfirmed. FIG. 13 shows STEM photographs of cross-sectional viewsshowing steps of forming spacers having a flat top from a two-layer filmin steps (a) to (f). In (a), a template was prepared and a SiN/SiOtwo-layer film was formed in a manner substantially similar to that inExample 5. In (b), the outer SiO layer was etched and the inner SiNlayer was about to be exposed. After the inner SiN layer was almostexposed (e.g., immediately after (b)), the etching conditions wereswitched from those for SiO (Table 9) to those for SiN (Table 11). Whilethe dry etching by ion bombardment progressed, the top portions of theouter and inner layers were removed in (c), and due to the difference indry etch rate (DER) between the inner and outer layers (DER of the innerlayer was higher than that of the outer layer under the etchingconditions), the top of the outer layer became pointed as shown in acircle in (c). Ions were reflected on an exposed surface of the innerlayer and bombarded the pointed portion of the outer layer, therebyremoving the tip of the outer layer and flattening the top of the outerlayer as shown in a circle in (d), while the exposed surface of theinner layer was etched. In (d), the top of the inner layer was alsoflattened. This may be because an inner portion of the inner layer wasmore damaged than an outer portion of the inner layer due toaccumulation of plasma bombardment while the inner layer was deposited(the inner portion was exposed to a plasma for a longer time than wasthe outer portion). Thereafter, the ashing process was conducted toremove a core material 101 as shown in (e). The final profile of theresultant spacers is shown in (f). In this example, the leaning angle ofthe spacers was 1.5 degrees. As described above, by manipulating adifference in dry etch rate between the inner and outer layers, the topof spacers can be made substantially flat, and further, by manipulatingfilm stresses of the inner and outer layers, spacers having a desiredleaning angle can be formed. These spacers are highly useful andadvantageous for SDDP or SADP, and any other semiconductor fabricationprocesses.

It will be understood by those of skill in the art that numerous andvarious modifications can be made without departing from the spirit ofthe present invention. Therefore, it should be clearly understood thatthe forms of the present invention are illustrative only and are notintended to limit the scope of the present invention.

1. (canceled)
 2. The method according to claim 14, wherein the conformalpattern-transfer film is constituted by multiple layers.
 3. The methodaccording to claim 13, wherein the second leaning angle is in a range ofapproximately −1° to approximately 1°.
 4. The method according to claim13, wherein the multiple layers are deposited by plasma-enhanced atomiclayer deposition (PEALD).
 5. The method according to claim 2, whereinthe multiple layers are constituted by a first layer and a second layerdeposited on the first layer, wherein the first layer has a film stresswhich is more compressive than a film stress of the second layer, andthe first layer has a thickness which is 25% to 75% of a total thicknessof the first and second layers.
 6. The method according to claim 2,wherein the multiple layers are constituted by a first layer and asecond layer deposited on the first layer, wherein the first layer has afilm stress which is more compressive than a film stress of the secondlayer, and the thickness of the first layer is equal to or greater thanthe thickness of the second layer.
 7. The method according to claim 13,wherein a difference between the film stress of the first layer and thefilm stress of the second layer is between approximately 150 MPa andapproximately 800 MPa.
 8. The method according to claim 13, wherein thefirst and second layers are independently constituted by silicon oxideor silicon nitride.
 9. The method according to claim 8, wherein thefirst layer is constituted by silicon nitride and the second layer issilicon oxide.
 10. The method according to claim 8, wherein the firstand second layers are constituted by silicon oxide.
 11. The methodaccording to claim 13, wherein the first and second layers areconstituted by different compositions.
 12. The method according to claim5, wherein the first layer has less resistance to dry etching than doesthe second layer.
 13. A method of forming spacers for spacer-definedpatterning in steps comprising (i) depositing a pattern-transfer film ona template having a surface patterned by a mandrel formed on anunderlying layer, (ii) dry-etching the template whose entire uppersurface is covered with the pattern-transfer film, and therebyselectively removing a top portion of the pattern-transfer film formedon a top of the mandrel and a horizontal portion of the pattern-transferfilm formed on the underlying layer while leaving the mandrel as a corematerial and sidewall portions of the pattern-transfer film formed onsidewalls of the mandrel as spacers, and (iii) dry-etching the corematerial, forming a vacant space, whereby the template has a surfacepatterned by the spacers on the underlying layer, which spacers leaninwardly toward the vacant space at a first leaning angle which isdefined as an angle of an inner face of each sidewall portion asmeasured with reference to a line vertical to a bottom of the vacantspace wherein a leaning angle of zero represents completely vertical anda leaning angle of a positive value represents leaning inward, whereinthe improvement comprises: in step (i), depositing, as thepattern-transfer film, a conformal pattern-transfer film havingdifferent film stresses in a depth direction wherein a lower half of theconformal pattern-transfer film has a first film stress and an upperhalf of the conformal pattern-transfer film has a second film stress,wherein the first film stress is more compressive than the second filmstress, whereby in step (iii), the spacers lean inwardly toward thevacant space at a second leaning angle which is less than the firstleaning angle, wherein: the conformal pattern-transfer film isconstituted by a first layer and a second layer deposited on the firstlayer, wherein the first layer has a film stress which is morecompressive than a film stress of the second layer, and the first layerhas a thickness which is 25% to 75% of a total thickness of the firstand second layers, the first layer has less resistance to dry etchingthan does the second layer, and a difference in resistance to dryetching between the first layer and the second layer is such that instep (ii), a top of each spacer becomes substantially flat by inhibitingshoulder loss of the spacer by dry etching.
 14. A method of formingspacers for spacer-defined patterning in steps comprising (i) depositinga pattern-transfer film on a template having a surface patterned by amandrel formed on an underlying layer, (ii) dry-etching the templatewhose entire upper surface is covered with the pattern-transfer film,and thereby selectively removing a top portion of the pattern-transferfilm formed on a top of the mandrel and a horizontal portion of thepattern-transfer film formed on the underlying layer while leaving themandrel as a core material and sidewall portions of the pattern-transferfilm formed on sidewalls of the mandrel as spacers, and (iii)dry-etching the core material, forming a vacant space, whereby thetemplate has a surface patterned by the spacers on the underlying layer,which spacers lean inwardly toward the vacant space at a first leaningangle which is defined as an angle of an inner face of each sidewallportion as measured with reference to a line vertical to a bottom of thevacant space wherein a leaning angle of zero represents completelyvertical and a leaning angle of a positive value represents leaninginward, wherein the improvement comprises: in step (i), depositing, asthe pattern-transfer film, a conformal pattern-transfer film havingdifferent film stresses in a depth direction wherein a lower half of theconformal pattern-transfer film has a first film stress and an upperhalf of the conformal pattern-transfer film has a second film stress,wherein the first film stress is more compressive than the second filmstress, whereby in step (iii), the spacers lean inwardly toward thevacant space at a second leaning angle which is less than the firstleaning angle, wherein the conformal pattern-transfer film has filmstress varying in the depth direction, wherein the film stress graduallyincreases in an outward direction.
 15. (canceled)
 16. (canceled) 17.(canceled)
 18. A method of forming vertical spacers for spacer-definedmultiple patterning, comprising: (i) providing a template having asurface patterned by a mandrel formed on an underlying layer in areaction space; (ii) depositing a first conformal pattern-transfer filmhaving a first film stress, and continuously depositing a secondconformal pattern-transfer film having a second film stress on theentire patterned surface of the template, wherein the first and secondfilm stresses are different; (iii) dry-etching the template whose entireupper surface is covered with the first and second pattern-transferfilms, and thereby selectively removing a portion of the first andsecond pattern-transfer films formed on a top of the mandrel and ahorizontal portion of the first and second pattern-transfer films whileleaving the mandrel as a core material and a vertical portion of thefirst and second pattern-transfer films as vertical spacers; and (iv)dry-etching the core material, forming a vacant space between thevertical spacers, whereby the template has a surface patterned by thevertical spacers on the underlying layer, the method further comprises:(v) measuring a leaning angle of the vertical spacer, which is definedas an angle of an inner face of the vertical spacer facing the vacantspace as measured with reference to a line vertical to a bottom of thevacant space wherein a leaning angle of zero represents completelyvertical and a leaning angle of a positive value represents leaninginward, followed by judging whether the leaning angle is within a targetrange; (vi) conducting again steps (i) to (iv): (a) without changes toform final vertical spacers if the leaning angle is within the presetrange; (b) with changes wherein, as the first conformal pattern-transferfilm in step (ii), a conformal pattern-transfer film having highercompressive stress than the first film stress by a measurable degree isdeposited, and/or, as the second conformal pattern-transfer film in step(ii), a conformal pattern-transfer film having higher tensile stressthan the second film stress by a measurable degree is deposited, if theleaning angle is greater than the preset range; or (c) with changeswherein, as the first conformal pattern-transfer film in step (ii), aconformal pattern-transfer film having lower compressive stress than thefirst film stress by a measurable degree is deposited, and/or, as thesecond conformal pattern-transfer film in step (ii), a conformalpattern-transfer film having lower tensile stress than the second filmstress by a measurable degree is deposited, if the leaning angle issmaller than the preset range; and (vii) repeating steps (v) and (vi)after increasing the measurable degree used in (b) or (c), if (b) or (c)in step (vi) is conducted, wherein the first conformal pattern-transferfilm has a first resistance to dry etching, and the second conformalpattern-transfer film has a second resistance to dry etching; and step(v) further comprises judging whether a top of the vertical spacer issubstantially flat, wherein if the top of the vertical spacer is notsubstantially flat; in step (vi), as the first conformalpattern-transfer film, a first conformal pattern-transfer film which hasless resistance to dry etching than the first resistance to dry etchingand also than the second conformal pattern-transfer film by a measurabledegree is deposited, and/or, as the second conformal pattern-transferfilm, a second conformal pattern-transfer film which has higherresistance to dry etching than the second resistance to dry etching andalso than the first conformal pattern-transfer film by a measurabledegree is deposited; and in step (vii), steps (v) and (vi) are repeatedafter increasing the measurable degree, until the top of the verticalspacer is substantially flat.
 19. A method of forming spacers forspacer-defined patterning in steps comprising (i) depositing apattern-transfer film on a template having a surface patterned by amandrel formed on an underlying layer, (ii) dry-etching the templatewhose entire upper surface is covered with the pattern-transfer film,and thereby selectively removing a top portion of the pattern-transferfilm formed on a top of the mandrel and a horizontal portion of thepattern-transfer film formed on the underlying layer while leaving themandrel as a core material and sidewall portions of the pattern-transferfilm formed on sidewalls of the mandrel as spacers, and (iii)dry-etching the core material, forming a vacant space, whereby thetemplate has a surface patterned by the spacers on the underlying layer,wherein a shoulder part of each spacer facing the vacant space, whichshoulder part is an outer corner of a top of the spacer, is lost oretched, forming an inclined surface from an outer side to an inner sideof the top of the spacer, wherein the improvement comprises: in step(i), depositing, as the pattern-transfer film, a conformalpattern-transfer film constituted by a two-layer film including a firstlayer and a second layer deposited on the first layer wherein the firstlayer has less resistance to dry etching than the does second layer,wherein a difference in resistance to dry etching between the firstlayer and the second layer is such that in step (iii), the top of eachspacer becomes substantially flat by inhibiting shoulder loss of thespacer by dry etching.
 20. The method according to claim 19, wherein thefirst layer is constituted by silicon nitride, and the second layer isconstituted by silicon oxide.